Process for the manufacture of phenylhydrazine

ABSTRACT

A PROCESS FOR THE MANUFACTURE OF PHENYLHYDRAZINE BY CATHODIC REDUCTION WITH SEPARATION OF CATHODE AND ANODE SPACES BY A DIAPHRAGM WHEREIN DIAZOAMINOBENZENE DISSOLVED IN AN ELECTROLYTE IS REDUCED ON SOLID ELCTRODES.

United States Patent ()fice 3,836,440 Patented Sept. 17, 1974 3,836,440PROCESS FOR THE MANUFACTURE OF PHENYLHYDRAZINE Hartmuth Alt, deceased,late of Munich, Germany, by

Ortwin Franz Felix Alt, Straubing, and Gudrun Anneliese Beyer nee Alt,Hohensachsen, near Weinheim, executors, and Hermann Clasen, Falkenstein,Taunus, and Jurgeu Cramer, Frankfurt am Main, Germany, assignors toFarbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning,Frankfurt am Main, Germany No Drawing. Filed Nov. 20, 1972, Ser. No.307,776 Claims priority, application Germany, Nov. 20, 1971, P 21 57608.9 Int. Cl. C07b 29/06; C07c 109/04 US. Cl. 204--74 5 Claims ABSTRACTOF THE DISCLOSURE A process for the manufacture of phenylhydrazine bycathodic reduction with separation of cathode and anode spaces by adiaphragm wherein diazoaminobenzene dissolved in an electrolyte isreduced on solid electrodes.

The present invention relates to a process for the manufacture ofphenylhydrazine.

The electrolytic reduction of hydrochloric acid solutions of benzenediazonium chloride to yield phenylhydrazine is known. (P. Riietschi, G.Triimpler in Helvetica 36 (1953) pages 1649-1658). To avoid secondaryreactions of the phenylhydrazine formed, the solution must be pressedfrom below through the mercury cathode at 5 C., a process which is notoverly attractive from a technical point of view because of the lowspace-time yields.

It is also known that the reduction of benzene normal diazotate inalkaline solution at 0-5 C. takes place with low yields ofphenylhydrazine (F. Fichter, E. Willi in Helvetica I7 (1934) page 1418).Good yields can be obtained after rearrangement into the anti-derivativebut only at a temperature below C., which involves cooling problems.

The technical accomplishment of the diazotate reduction is additionallyimpeded by the fact that it is an indirect electro-chemical reduction(F. Fichter, Organische Elektrochemie 1942, page 223). The diazotate isnot reduced directly by the absorption of electrons from the cathode butby the cathodically produced sodium amalgam. It is therefore notsurprising that poor yields are obtained when other cathode materialsthat are better suited for a technical performance are used in thereduction of aromatic diazotates (F. Fichter, E. Willi in Helvetica 17(1934) page 1418).

It is likewise known that in the polarographic reduction on the droppingmercury electrode diazoaminobenzene accepts 4 electrons and 4 protons.It is said that in this reaction phenylhydrazine and aniline are formed(as to the protonation problems in electrode processes conferInvestigations With Diazoaminobenzenes and Unsaturated Ketones"L.Holleck; Elektrochemisches Symposium der GDCh of Oct. 13-15, 1971 in theNuclear Research Plant Jiilich).

Still further it is known that phenylhydrazine undergoes relatively easyreductive scission. With hydrogen on nickel, aniline and ammonia areobtained in a quantitative yield at atmospheric pressure and normaltemperature. (H. Rupe, E. Hodel in Helvetica 6 (1923) page 873). Withzinc and hydrochloric acid the quantitative scission of phenylhydrazinecan also be obtained (E. Fischer, Liebigs Annalen 239 (1887) page 248).

In the electrochemical reduction of aromatic diazotates on lead orcadmium the escape of ammonia indicates the cathodical scission of thehydrazine grouping; therefore, the yields of arylhydrazine are only inthe range of from 20-27%, whereas under identical conditions on mercurya yield of over of phenylhydrazine can be reached. (F. Fichte, E. Williin Helvetica 17 (1934) page 1418).

It has now surprisingly been found that phenylhydrazine can be obtainedby cathodic reduction in a good yield by reducing diazoaminobenzene,dissolved in an electrolyte on solid electrode materials such as lead,zinc, zinc-titanium alloy, cadmium, tin and surprisingly also copper andgraphite. It is known that copper and graphite have a distinctly lowerhydrogen over-voltage than, for example, lead or mercury and, therefore,they ought to be less suitable for the reduction of diazoaminobenzene.Nevertheless, the use of copper or graphite as electrode material givesvery high yields of phenylhydrazine even in galvanostatic electrolysis,i.e. under technically interesting conditions.

In contradistinction to the cathodic reduction of diazonium salts anddiazotates, the electrolysis tempera ture can be varied in a wide rangeand its upper limit is only given by the thermal decomposition of thediazoaminobenzene. A temperature in the range of from '20 to C.,especially +15 to +60 C. is preferred. The electrolysis is preferablycarried out with aqueous electrolytes. To improve the solubility of thediazoaminobenzene in the catholyte the common solvents such as alcohols,ethers, carboxylic acid amides and/or nitriles or mixtures thereof aresuitably added as organic cosolvents.

The diazoaminobenzene can be prepared either before-hand according toknown processes in a separate reaction or directly in the catholyte fromaniline. Besides the high yield and the largely variable electrolysistemperature, the process of the invention therefore has the furtheradvantage that the aniline obtained in the cathodic dissociation ofdiazoaminobenzene can be used again for preparing freshdiazoaminobenzene.

A sufiicient conductibility of the catholyte is preferably obtained inknown manner by adding suitable conducting salts. The pH-value of thecatholyte has to be chosen in such a manner that the diazoaminobenzenecannot be split to give benzenediazonium salt and aniline, a pH- valueabove 5, especially about 6 to 14 being preferred. Higher pH-values arealso possible but they do not offer any advantage. Suitable conductingsalts are preferably alkali metal and ammonium hydroxides as well asorganic bases, for example the various tetraalkyl ammonium hydroxides.

As electrolysis cells there can be used all common cells with separationof cathode and anode space by diaphragms. As diaphragms there can beused all common materials provided that they are stable to alkali and/oracids as well as the used organic solvents. Especially suitable are ionexchange diaphragms, more particularly anion exchange diaphragms.

In the following examples the yields of phenylhydrazine were obtainedwithout choosing the optimum conditions. It is obvious that by variationof the electrolysis conditions better yields can be obtained. Thephenylhydrazine can be obtained not only in the form of thehydrochloride as described in the following examples but also byseparation from the aniline without acidifying the catholyte, forexample by distilling off the solvent from the catholyte directly andworking up by distillation the mixture of phenylhydrazine and anilinethen separating.

The material yields are calculated on the amount of diazoaminobenzeneused as in the chosen acid working-up of the catholyte, this is resplitinto benzenediazonium salt and aniline so that the unreacted portion ofthe starting substance is not determined directly.

3 EXAMPLE *1 The electrolysis was carried out in' the presence of aninert gas in a round glass cell having a capacity of about 350 ml. andprovided with cooling jacket on a lead disc of about 45 cm Stirring wasperformed with a magnetic stirrer, the rotating core of which rested onthe disc. The cell Was provided with a lateral neck for inserting aLuggin-capillary for the reference electrode (silver/silver chloride).The anode space consisted of a polyethylene tube having a lower diameterof about cm., which tube was closed at the lower end by an anionexchange diaphragm (Nepton A111 BZL 183) by means of a screw collarring. The opposite end of the tube was screwed into a polyethylenestopper provided with standard ground joint so that the cell was tightlyclosed. The stopper had the necessary standard ground borings forthermometer, bubble counter and inert gas inlet. As anode a stainlesssteel (V4A)spiral was used. The anolyte was 3 N KOH.

The catholyte contained 0.1 mol (19.7 g.) diazoaminobenzene dissolved in200 ml. of a mixture of methanol/ 3 N KOH in a ratio of 20:1. Theelectrolysis temperature was in the range of from 2833 C. 10.7 a./h r.of current were passed potentiostatically at l800 mv. (against Ag/AgCl)through the cell, whereupon the initially deep blackish rednontransparent solution had turned pink.

The solution was acidified with HCl, methanol was distilled 011, theresidue was taken up in concentrated hydrochloric acid and thephenylhydrazine hydrochloride remaining as a precipitate was filtered01f with suction. The salt was suspended in water, the suspension wasrendered alkaline with NaOH whereby the free phenylhydrazine separated.It was repeatedly extracted with ether, the combined ether phases weredried and the ether was distilled 011. 10.2 g. of phenylhydrazine wereobtained.

The filtrate remaining behind after the separation of thephenylhydrazine hydrochloride was rendered alkaline with NaOH and theseparated aniline was extracted with ether. After drying and distillingoff of the ether 8.85 g. aniline were obtained. The yield of 10.2 g. ofphenylhydrazine cor responds to a material yield of 94% or a currentefiiciency of 94%.

EXAMPLE 2 EXAMPLE 3 Electrolysis was carried out in the cell describedin Example 1, with the exception that an electrographite disc having asurface of 40 cm. was used. 11.5 a./hr. were passed galvanostatically at2 ampere through the mixture consisting of 200 ml. methanol/3 N KOH(20:1) and 19.7 g. (0.1 mol) diazoaminobenzene. The material yield ofphenylhydrazine was 89%, the current efficiency 83%.

EXAMPLE 4 EXAMPLE 5 Electrolysis was carried out in a flow cellconsisting of 2 equally large square polyethylene halves between whichthe anion exchange diaphragm (commercial name Nepton A 111 BZL 183) wasclamped. The etfective cathode surface was 115 cm. To obtain a uniformsubstance transport the electrode spaces were divided in fourtrajectories by conducting strips resting on the electrodes and thediaphragm. The distance cathode to diaphragm was 6 mm. Lead was used ascathode material, platinum as anode material.

The electrolytes (anolyte: 700 ml. 3 N KOH; catholyte: 1000 ml. 0.5molar diazoaminobenzene in methanol/ 3 N KOH (20:1)) were circulated bya pump with a flow speed of about 15 cm. per second. 6.7 a./hr. currentwere passed galvanostatically at 18 amperes. The reaction mixture wasworked-up as in Example 1 whereby phenylhydrazine was obtained in amaterial yield of 91.5% or a current efliciency of 73%.

Phenylhydrazine is a valuable intermediate product and starting productfor pharmaceutical and dyestuffs.

What is claimed is:

1. Process for the manufacture of phenylhydrazine by cathodic reductionwith separation of cathode and anode spaces by diaphragm which comprisesreducing at a cathode selected from the group consisting of cadmium,copper, graphite, lead, tin, zinc and an alloy of zinc and titaniummaterial diazoaminobenzene dissolved in an electrolyte comprising water,an organic cosolvent, and a conductive compound selected from the groupconsisting of alkali metal hydroxide, ammonium hydroxide, an organicbase and mixtures thereof at a pH above 5 and a temperature between 20to C.

2. The process of claim 1, wherein graphite is used as cathode material.

3. The process of claim 1 wherein the pH of the electrolyte is above 6.

4. The process of claim 1, wherein the conducting compound is an alkalimetal hydroxide.

5. The process of claim 1, wherein an ion exchange material is used asdiaphragm.

References Cited UNITED STATES PATENTS 3,267,011 8/1966 Moore 204 74FOREIGN PATENTS 1,961,364 '6/1971 Germany 204-74 FREDERICK C. EDMUNDSON,Primary Examiner

